Field of the Invention
The present invention relates to a substrate for a liquid ejection head for ejecting liquid, such as ink, the liquid ejection head, a liquid ejection apparatus, and a method for ejecting liquid.
Description of the Related Art
An example of the liquid ejection apparatus is an ink-jet printer that ejects liquid ink from a print head serving as a liquid ejection head to print an image. Such a printer ejects ink using ejection-energy generating elements, such as electro-thermal transducers (heaters) and piezoelectric elements. For example, with the heaters, the printer causes ink to generate bubbles using heat generated by the heaters and ejects the ink through ejection ports using the energy of generating bubbles.
Japanese Patent Laid-Open No. 2010-155452 discloses a configuration in which the gate voltage of a PMOS transistor connected to one end of each heater and the gate voltage of an NMOS transistor connected to the other end of the heater are individually controlled by individual voltage conversion circuits to stabilize a voltage for driving the heater. These voltage conversion circuits are installed in a print head substrate together with the PMOS transistors, the NMOS transistors, and the heaters.
The print head substrate described in Japanese Patent Laid-Open No. 2010-155452 includes a plurality of PMOS transistors and a plurality of NMOS transistors corresponding to the individual plurality of heaters. The print head substrate further includes a plurality of voltage conversion circuits corresponding to the plurality of PMOS transistors and a plurality of voltage conversion circuits corresponding to the plurality of NMOS transistors. However, to install the plurality of transistors and the plurality of voltage conversion circuits in the print head substrate, it is difficult to ensure a sufficient space therefor. For example, to dispose transistors and voltage conversion circuits between two arrays of heaters corresponding to two arrays of ejection ports requires a large distance between the two arrays of heaters, making it difficult to form the print head substrate within a desired size. Reducing the size of the transistors to form the print head substrate in a desired size can lead to severe limitation on the heater current because of the characteristics of the common-drain transistors and can reduce the voltage applied to the heaters, leading to a decrease in ink ejection efficiency.